Biological N2 fixation in the upwelling region off NW Iberia: magnitude, relevance and abundance of diazotrophs.
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AuthorsMoreira-Coello, V.; Mouriño-Carballido, B.; Marañón, E.; Fernández-Carrera, A.; Bode, A.; Varela, M.M.
nitrate diffusive flux
NW Iberian upwelling
The classical paradigm about marine N2 fixation establishes that this process is mainly constrained to nitrogen-poor tropical and subtropical regions, and sustained by the colonial cyanobacterium Trichodesmium spp. and diatom-diazotroph symbiosis. However, the application of molecular techniques allowed determining a wide distribution and high phylogenic diversity of marine diazotrophs, which extends the range of marine environments where biological N2 fixation may be relevant. Between February 2014 and December 2015, we carried out 10 one-day samplings in the upwelling system off NW Iberia in order to: 1) investigate the seasonal variability in the magnitude of N2 fixation, 2) determine its biogeochemical role as a mechanism of new nitrogen supply, and 3) quantify the main diazotrophs in the region under contrasting hydrographic regimes. Our results indicate that the magnitude of N2 fixation in this region was relatively low (0.001±0.002 – 0.095±0.024 µmol N m-3 d-1), comparable to the ...
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